New method to determine restrained-shrinkage stresses in propellant-grain models

This paper deals with the photoelastic determination of restrained-shrinkage stresses which may be produced by curing or by thermal effects in models of solid propellant grains bonded to the case. Use is made of the birefringence exhibited in the curing process of a restrained polyurethane rubber. The techniques developed to take advantage of this property are shown in detail. The method can also be applied to the determination of the residual stresses produced in the curing process of a propellant cast around a rigid insert. An example of this application is also given. The extension of the method, using epoxies, to three-dimensional analyses is pointed out.     

Normalized stresses around an elliptic hole in a finite plate of linear material subjected to large uniform in-plane loading

Stress-concentration factors associated with the large deformations of in-plane loaded plates with elliptic holes are presented in a form with which designers are familiar. An analytic expression to obtain the stress-concentration factor is included.     

Elastoplastic analysis of a bent circular plate with a central hole

A circular aluminum plate with a small concentric hole (1/10 the plate thickness) and supported on its outer edge by a ring was subjected to a concentrated load at its center, applied through a rigid ball of radius equal to the plate thickness. Strains were determined using grids, moiré, and electrical strain gages on the top and bottom surfaces of the plate for loads up to and including the one associated with the appearance of the first crack in the plate. The investigation is related to the development of specimens to be used to determine fracture characteristics of materials used in lightweight construction.     

On the definitions of strain and their use in large-strain analysis

It is pointed out that when strains are computed from a displacement field, the engineering definition of strain(l _f ?l _i )/l _i has advantages in respect to other definitions used in finite-strain theory. Tensorial transformations can still be used easily by means of Mohr's circle. Illustrations for the case of Eulerian and Lagrangian strains are shown. The comments may be of particular interest to experimental analysts.     

Maximum stress at the angular corners of long strips bonded on one side and shrunk

The value of the maximum stress, and its position, at the corner of long strips bonded on one side and shrunk, has been determined using photoelasticity. The angle of the strip end varies from zero (crack) to 180 deg (no corner). The radius at the corner varies from less than 0.0001 to 0.125 in. The solution obtained is an approximation to a plane-stress solution and will have application in composite-materials problems (coatings, solid-propellant rocket grains, etc.).     

Determination of loads applied perpendicularly to the outer boundary of a ring using coefficients of influence

A procedure is explained to determined the amount of several pairs of diametrical loads applied to the outside boundary of a ring when stresses at selected points of the inside or outside boundaries are known. Coefficients of influence are used, following an approach similar to the one presented in a previous paper. Examples of application are given and the possible increase in precision is shown when the number of points of measurements is larger than the number of loads to be determined.